1. Field of the Invention
The present invention relates to a compact zoom lens system and, in particular, to a zoom lens system designed specially to be compact with its whole optical system, being suitable for such as a digital still camera.
2. Related Background Art
In an image gathering system using a solid-state imaging device, in order to arrange a low-pass filter or a color correction filter, a lens system having a relatively long back focal length is required. Moreover, a lens system having a good telecentricity on an image side is required. In these days, compactness and low cost are also required to a lens system in addition to satisfying these requirements.
These lens systems described above have been proposed, for example, in Japanese Patent Application Laid-Open No. 10-293253 and in Japanese Patent Application Laid-Open No. 2001-013408.
In Japanese Patent Application Laid-Open No. 10-293253, a three-lens-group zoom lens system having, in order from an object side, a first lens group having negative refractive poser, a second lens group having positive refractive power, and a third lens group having positive refractive power wherein zooming from a wide-angle end state to a telephoto end state is carried out by moving the first lens group and the second lens group, has been proposed.
Japanese Patent Application Laid-Open No. 2001-013408 proposes a variable focal length lens system having construction that reduces the number of lens elements in a first lens group.
However, the zoom lens system proposed in Japanese Patent Application Laid-Open No. 10-293253 has drawbacks such as relatively large number of lens elements composing each lens group, relatively large total lens length, and higher manufacturing costs.
Moreover, Japanese Patent Application Laid-Open No. 2001-013408 discloses an optical system in which a positive lens element is arranged on the most object side of a first lens group having negative refractive power. Accordingly, it has a drawback that the diameter of the lens system inevitably becomes large when the system is made to have a wider angle of view. Furthermore, since the first lens group separates largely from the aperture stop in the wide-angle end state, the height of an off-axis ray incident to the first lens group becomes large, so that the diameter of the lens composing the first lens group becomes large. As a result, the lens system has a drawback that the whole lens system becomes large.